The invention generally relates to the monitoring of parameters, particularly but not exclusively temperature, in the subsea environment and along (either interior or exterior to) a relevant temporary landing string or riser assembly. The invention also relates to using a distributed temperature system to determine whether solids have formed in the surroundings of a pipeline or wellbore.
At various times during the life of a subsea well, a temporary marine riser is located between a blow out preventer (BOP) and a platform at the ocean surface. The BOP is located at the ocean bottom. In instances when a vertical Christmas tree will be used, a BOP is installed for the drilling and completion stages of the well. Thereafter, the BOP is removed and the vertical Christmas tree is installed, until intervention of the well is required at which time the vertical tree is removed and the BOP is reinstalled. In instances when a horizontal Christmas tree will be used, a BOP is installed for the drilling stage of the well. Thereafter, the BOP is removed and the horizontal Christmas tree is installed with the BOP on top of it. The well is then completed and tested with the BOP installed on top of the horizontal tree. Further intervention is also conducted through the BOP on top of the horizontal tree. In any of the cases when the well is being drilled, completed, or tested, a temporary landing string may be deployed within the marine riser and within the BOP.
It is important to control and monitor temperature at the BOP as well as along the marine riser. Unacceptably high temperatures could compromise the safety systems of the BOP or landing string. Unacceptably low temperatures could provide an indication of hydrate formation or increased likelihood of wax deposition. Prior art systems used to obtain this information involve running separate pods and electrical lines to obtain a single point of measurement. These prior art techniques are not capable of providing temperature measurements at multiple points along the BOP and/or marine riser.
For example, when produced, hydrocarbons tend to have a high temperature. On the other hand, the marine riser, since it is surrounded by ocean water, tends to have a low temperature. Due to this temperature difference as well as the presence of other variables, hydrates, or other solids, sometimes form within the marine riser. The formation of hydrates in the marine riser in turn may cause blockage of flow and hold-up of intervention equipment, which could lead to a significant loss of money and time and may compromise safety systems. The ability to monitor the temperature at various points along the marine riser would provide an operator the ability to predict and avoid, through appropriate chemical injection for example, the formation of hydrates within the marine riser. Moreover, the ability to monitor temperature at various points along the marine riser would also provide an operator the ability to determine the position and extent of any hydrate blockage, which would enable the operator to educatedly establish a course of action.
Solids, such as waxes or hydrates, may also form in other pipelines, including subsea and industrial process pipelines, or in land wells. The ability to monitor temperature at various points along these structures would provide an operator the ability to determine the position and extent of any solid blockage, which would enable the operator to take corrective action.
Thus, there exists a continuing need for an arrangement and/or technique that addresses one or more of the problems that are stated above.